Patients with partial or complete paralysis or muscular weakness of the extremities often are assisted in mobility by the use of an orthotic device or orthosis. For example, a patient with weakness of leg muscles may employ an orthosis to provide assistance in supporting body weight during the stance phase of the gait cycle.
A knee, ankle, and foot orthosis (KAFO) typically extends from the patient's upper leg to the lower leg, and provides a foot support. In order to accommodate normal flexion of the patient's knee, a knee joint or hinge joins an upper portion of the KAFO (which is worn attached to the patient's upper leg) to a lower portion of the KAFO (which is worn attached to the patient's lower leg). Additionally, an ankle joint may be provided between the lower portion and the foot support to allow, or control, flexion of the foot.
One common aspect of a knee orthotic, including a KAFO, is the ability to lock the knee joint or hinge in a straight legged position so that the rigidly locked KAFO supports the patient in stance in compensation for weakness or paralysis of the leg muscles.
Various devices have been devised for locking the knee hinge or joint of an orthosis such as a KAFO. However, while it is advantageous to lock the knee for support during stance, it is problematic for the knee to remain locked during the swing phase of the gait cycle.
With an orthotic knee continuously locked, a patient must perform an unnatural and inefficient motion to affect a walking gait, by lifting the leg with the orthosis to provide for clearance of the foot from the ground as the leg swings forward.
Further, in the case of a KAFO, it is more likely that the patient wearing the KAFO suffers from a weakness or abnormality in muscles related to dorsal or plantar flexion of the foot. A patient who has, for example, weakened dorsal flexors of the foot may lack the ability for proper dorsal flexion of the foot during the gait cycle, in addition to lacking leg strength for support. As a result, gait problems resulting from a rigidly locked orthotic knee may be exacerbated by an inability of the patient to dorsally flex the foot and thereby raise the toes to avoid toe drag during the swing phase of the gait.
In addition to the leg lift required for clearance in the leg with a locked knee, further lifting may be required for clearance of the toes or forefoot. Not only does a further awkwardness or inefficiency of the gait result, a safety consideration arises in the increased risk of fall due to toe drag if sufficient clearance is not consistently achieved.
It is therefore desirable for an orthotic knee joint to be selectively lockable, so that support may be provided during the stance phase while knee flexion is allowed during the swing phase to facilitate a more normal, and more efficient, gait. Further, in the case of a KAFO, it is desirable for ankle and knee compensation strategies to be coordinated in function so that the patient's gait is additionally improved.
In addition to gait problems that result from a continuously locked knee, a knee that is rigidly locked does not provide shock absorption that may be achieved by even a small degree of flexion of the knee.